Lack of adequate numbers and normal function of blood platelets is associated with many disease processes, and can cause debilitating and life threatening blood loss. Thus far, the only effective treatment for these patients has been to transfuse them with donated blood products containing large numbers of viable platelets. This treatment, however, is associated with various problems of supply and safety. Platelets are fragile, and should be separated from whole blood within eight hours. After collection donated platelets have at most only a several day lifespan, after which the platelets are discarded as "outdated." It may require as many as ten donors to obtain a sufficient quantity of platelets for a single transfusion to an adult patient. A large supply of donated blood is required to sustain each patient needing platelet replacement therapy. Because of the short platelet shelf life, and the difficulty of obtaining sufficient donated blood from which to isolate platelets, shortages of fresh platelets are common, with dire consequences for afflicted patients.
The transfusion of fresh platelets has raised safety issues. Infected donor platelets have transmitted hepatitis and AIDS. While improved tests for these viruses have greatly lowered the transmission rate, the tests still cannot ensure complete detection of all infected blood products.
Given the problems of platelet availability and safety, a safe and readily available transfusable platelet substitute with hemostatic function would provide substantial benefits for many patients. Producing a platelet substitute which preserves the hemostatic functions of the native platelet has been difficult due to the complex nature of the platelet. The platelet membrane has many components including lipids, proteins, and carbohydrates, all of which may be involved in the hemostatic function of the cell.
Although investigators have formed reconstituted vesicles carrying platelet glycoproteins, such reconstituted vesicles have been for use as basic research models, and did not involve evaluation of the hemostatic properties of the reconstituted membranes. Several recent publications have reported combining glycoproteins from platelets with purified phospholipids for the purpose of studying the function of platelet proteins in simplified artificial membrane structures. Partially purified platelet glycoproteins were inserted into simple phosphatidylcholine or phosphatidylcholine-phosphatidylserine liposomes by Sie et al. (1980), Parise and Phillips (1985), Baldasarre et al. (1985), and Rybak et al. (1988), none of which described using the products in animals.